Language teaching has always been in the center of attention for educators. As new methodologies emerge, the attitude towards EFL teaching changes and new ways are developed for making the teaching-learning process more effective. Vocabulary is one of the core aspects in any language. Its importance has been estimated by many scientists and it has been proved to play a crucial role in EFL acquisition. Authentic materials are believed to be effective tools for enlarging vocabulary. This study investigated the effectiveness of authentic vs. instructional materials on vocabulary acquisition. It draws parallels between the instructional and authentic materials by testing the effectiveness of each with the help of tests. The study was carried out over a period of ten weeks in an Armenian EFL setting. A number of instruments were used to collect and analyze the data, i.e. tests, questionnaires, interviews, etc. The findings and conclusions drawn from the experiment may help to make useful pedagogical implications and may be advantageous for EFL educators. The study also brings in more ideas for further research and experiment.